This invention relates to a high density packaging technique for electronics systems.
With the continuing increase in size and sophistication of electronic systems, such as large scale digital computers, the efficient cooling of densely packaged electronic components remains a very important design consideration. Recognition of the importance of this consideration has spurred development of several alternative techniques and approaches to the problems involved. For example, U.S. Pat. No. 4,019,098 shows a system for removing heat from integrated circuit modules which includes the use of heat pipes formed in a layered aluminum heat transfer structure which is mounted between a circuit board and the integrated circuit modules to be cooled. A similar approach using heat pipe technology is shown in U.S. Pat. No. 4,118,756. Other approaches to this problem are shown in U.S. Pat. Nos. 3,411,041, which describes a heat exchanger package designed to cool a number of circuit modules, and 4,327,399, which shows a heat pipe structure formed in a silicon or ceramic substrate upon which integrated circuit elements are mounted.
The continuing development of structures such as those described in these patents demonstrates the existence of a need for novel high density, thermally efficient packaging techniques. In particular, there exists a need for a high density packaging system which provides increases in space and thermal and manufacturing efficiencies, while permitting the use of conventional component and circuit board fabricating techniques.
Accordingly, an object of the present invention is to provide a high density packaging arrangement for electronic systems which is highly efficient with regard to component density and heat transfer characteristics, and which utilizes conventional manufacturing techniques and components.
The present invention comprises a plurality of circuit board assemblies, each having electrical components mounted on one side and cooling elements mounted on the other side, arranged such that the electronic components mounted on a first circuit board are in heat conductive contact with the cooling elements mounted on a second circuit board. The present invention further comprises an electronic component which comprises an electronic device encapsulated in a thermoplastic resin. A particularly advantageous embodiment of such a component for use with the present invention includes a high thermal conductivity element (i.e., an element whose thermal conductivity is high relative to the thermoplastic resin) partially encapsulated and held in place by the thermoplastic material, but having an exposed portion or surface for contacting the cooling elements of an adjacent board. This element is preferably made of metal and is preferably positioned on the electronic device in the mold prior to injecting the thermoplastic resin.
A particularly advantageous embodiment of the present invention results when the electronic components are mounted in recesses formed on one side of the circuit board and the cooling elements are mounted in channels formed on the other side of the circuit board. By so forming the circuit boards, electrical interconnection of the electronic components mounted on different boards is possible. This is accomplished by mounting conductive elements on the ridge areas formed between the recesses and channels, such that contact is established between conductive elements on adjacent boards when the packaging arrangement is assembled. This structure allows the electronic components mounted on different circuit boards to be electrically interconnected, while minimizing signal path and delay time and improving overall system performance.
Other aspects of the present invention include: the use of a removable support or clamping device such that the assembly can be readily disassembled for repair or replacement of defective parts; the use of compliant conductive elements, such as a conductive rubber contact element, for the mounting on the ridge areas of the boards; the placement of a resilient element, such as a rubber pad, between the electronic component and the circuit board to bias or push the electronic component toward the cooling element mounted on the adjacent board; and use of liquid or gaseous coolant in the coolant elements or tubes.